8 December 2005HIV Immune Response Different In Identical Twinsby George Atkinson

Developing a vaccine for AIDS may be much more difficult than many had previously thought, with new findings from UCLA showing that the immune systems in two HIV-positive identical twins responded to the infection in different ways. The findings, in the Journal of Virology, would seem to suggest that the body's defenses against the virus are random, rather than genetically determined.

The study was based on male twins who were infected by blood transfusions shortly after their birth in 1983. The twins were infected with the same strain of the virus and grew up exposed to the same environmental forces, making them ideal candidates for studying what should have been, identical immune system responses.

But paradoxically, the immune system reacted differently in each twin, showing that the body's defense response was random - and unpredictable.

"These boys are as similar as two humans can be, yet we see differences in how they fight the virus," said UCLA researcher Dr. Paul Krogstad. "That's one more thing that makes it difficult to develop a vaccine for everyone."

The key difference was the T-cell receptors (TCR), which play an important role in the immune system by binding viruses to receptors on their surface. HIV escapes this action by changing shape so that it does not fit into those receptors. While the twins' targeting of the HIV was remarkably similar, their overall TCR characteristics were highly divergent. Krogstad said this demonstrates that the interaction between their immune systems and the virus was random and unpredictable - indicating that a "one size fits all" vaccine may not be possible. "If the goal is to develop a vaccine, our findings suggest this may not be so straightforward," concluded co-researcher Dr. Otto Yang.

Based on material from University of California, Los Angeles (UCLA), Health Sciences